What happens when mixture of two gases is heated in a closed container?

If one gas expands faster than the other and increases pressure of the container enough so that the boiling point of the other gas is decreased below the gas temperature, will second gas start turning into liquid?

This phase change must also give out heat, causing the overall temperature and pressure to further increase.

Is this valid? or mixture of two gases work lot different than two of them separately?


1 Answer 1


You could certainly have such a situation; that is, heating two compounds in their gaseous state at constant volume such that that the total pressure of the system exceeds the vapor pressure of the lower boiling compound causing it to condense.

As the gas condenses, it will of course give off heat as you said, but it would require continued heat input to sustain the increasing pressure and condensation. I believe that is what you meant in your second question anyway.

  • 1
    $\begingroup$ It would be interesting to see if the increased volume due to the liquid phase taking up much less volume than it did in the gaseous phase would decrease the pressure too quickly to sustain the condensation. $\endgroup$
    – J. Ari
    Mar 30, 2017 at 2:22
  • $\begingroup$ Yea, a couple big and important unknowns in this scenario are the relative volumes of the gases and their enthalpies of vaporization. Do we have 98% of the original vapor as the non-condensing gas and only 2% is the condensing gas so that the decrease in total pressure isn't prohibitive? But then of course the partial pressure would be correspondingly small, so you need two gases with very different enthalpies of vaporization, with the condensing gas having a much higher vapor pressure. Would be fun to play with if I had the equipment and some ideas for the right gases...I have neither ;) $\endgroup$
    – airhuff
    Mar 30, 2017 at 3:12
  • $\begingroup$ oops, cc @J.Ari $\endgroup$
    – airhuff
    Mar 30, 2017 at 3:13

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